This invention relates to an applicator for "curtain-type pouring" or extruding of molten plastics material or the like, which applicator comprises two half shells constituting an applicator head and adapted for being spread apart in order to open the said head, and which applicator also comprises a slit-shaped pouring orifice, from which the molten plastics material is poured as a sheet or "curtain".
Such "curtain-type" extrusion is widely used nowadays for coating objects of many kinds. Thus, "curtain-type" pouring is applied, for instance, in the photographic industry when manufacturing photographic materials, for the lacquer-coating of wooden and metal plates and, more recently, also for coating electrical conductor-bearing plates, for distance with solder-stopping or solder-repelling lacquer or the like (see. e.g. U.S. Pat. No. 4,230,793).
In order to apply lacquer coatings to a substrate it is conventional to use an applicator having a slit-shaped extruding orifice. This is an applicator comprising an applicator head having an adjustable extruding orifice at its lowermost end, through which orifice coating mass emerges in dosified quantities, to descend, as a free-falling curtain, downwardly upon the substrate therebelow which is to be coated.
An applicator of this known type consists of two halves or shells which are connected at their top ends while, at their lower ends, there is provided with each half or shell, a blade-like ledge or bar, the extrusion orifice being formed between the opposing edges of the two ledges, whereby the breadth or width of the extrusion orifice can be adjusted by approaching the two applicator head halves toward each other, or spreading them apart. In order to clean the applicator head, one of the two halves can be pivoted upwardly, thereby opening the applicator head. In a similar type of known applicator, which is described in U.S. Pat. No. 3,832,427 (John Mutch), one of the two halves is stationary while the other can be pivoted about a hinge at its lower end, and the head can thus be opened by moving the pivotable half away from the stationary half, thereby also permitting adjustment of the width of the extrusion slot.
These known applicators suffer from various serious drawbacks. Thus, after each opening of the applicator head, the width of the extrusion orifice has to be adjusted anew, which is a critical and cumbersome operation, the accuracy depending on the care taken by the operating personnel. Moreover, in the first-mentioned and more frequently used applicator type, the adjustment of the width of the extrusion orifice can only be arrested in the closing direction, while there is no definite arresting means against unintentional widening of the extrusion orifice. Moreover, exchange of the ledges or "pouring lips" forming the pouring slit when one of them has become damaged, is a complicated operation which requires in each case a time-consuming and expensive re-adjustment. Furthermore, the length of the pouring slit cannot be altered without difficulty . As a further drawback, the known applicator head has movable faces that must be sealed against loss of molten plastics material during operation. These sealing faces must be finished by fine grinding at which leakages can frequently occur. Lacquer which penetrates into such leaking spots will harden and will then render it difficult to open the applicator head, causing damage to the polished faces. Finally, the first-mentioned known type of applicator requires a heavy structure welded from chromium steel parts, and is thus relatively expensive to manufacture.